19991789 has 2 divisors, whose sum is σ = 19991790. Its totient is φ = 19991788.

The previous prime is 19991753. The next prime is 19991791. The reversal of 19991789 is 98719991.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 10176100 + 9815689 = 3190^2 + 3133^2 .

It is a cyclic number.

It is not a de Polignac number, because 19991789 - 2²⁴ = 3214573 is a prime.

Together with 19991791, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 19991789.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (19991749) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9995894 + 9995895.

It is an arithmetic number, because the mean of its divisors is an integer number (9995895).

Almost surely, 2^19991789 is an apocalyptic number.

It is an amenable number.

19991789 is a deficient number, since it is larger than the sum of its proper divisors (1).

19991789 is an equidigital number, since it uses as much as digits as its factorization.

19991789 is an evil number, because the sum of its binary digits is even.

The product of its digits is 367416, while the sum is 53.

The square root of 19991789 is about 4471.2178430490. The cubic root of 19991789 is about 271.4046097697.

The spelling of 19991789 in words is "nineteen million, nine hundred ninety-one thousand, seven hundred eighty-nine".